Passive ranging of a target

Abstract

In an embodiment, an apparatus includes a detector and a range finder. The detector is configured to determine a direction to a target in response to a signal received from the target, and the range finder is configured to determine a range to the target in response to the direction and independently of an amplitude of the signal. For example, such an apparatus (e.g., a computer-based apparatus) may be disposed on tactical fighter aircraft, and may be able to range (e.g., azimuth range or slant range) a target passively even if an accurate measure of the amplitude of the signal received from the target is unavailable.

What is claimed is: 
     
       1. An apparatus, comprising:
 a detector configured to determine a direction to a target in response to a signal received from the target; and 
 a range finder configured to determine a range to the target in response to the direction and independently of an amplitude of the signal; 
 wherein the range finder is configured to determine the range to the target by: 
 tracking the target according to a first algorithm; 
 tracking the target according to a second algorithm; 
 weighting results of the first and second algorithms; and 
 determining the range to the target in response to the weighted results of the first and second algorithms. 
 
     
     
       2. The apparatus of  claim 1  wherein the direction includes an azimuth angle. 
     
     
       3. The apparatus of  claim 1  wherein the direction includes an elevation angle. 
     
     
       4. The apparatus of  claim 1  wherein the detector is configured to determine a direction to a moving target in response to a signal received from the moving target. 
     
     
       5. The apparatus of  claim 1  wherein the detector is configured to determine a direction to an approximately stationary target in response to a signal received from an approximately stationary target. 
     
     
       6. The apparatus of  claim 1  wherein the detector is configured to determine a direction to a target in response to a signal emitted from the target. 
     
     
       7. The apparatus of  claim 1  wherein the detector includes an electronic warfare system. 
     
     
       8. The apparatus of  claim 1  wherein
 the first algorithm is configured to model a path of the target as being an approximately straight line; and 
 the second algorithm is configured to model the path of the target as being a curved line. 
 
     
     
       9. The apparatus of  claim 1  wherein
 the first algorithm is configured to model the target as moving at an approximately constant velocity; and 
 the second algorithm is configured to model the target as moving at a changing velocity. 
 
     
     
       10. The apparatus of  claim 1  wherein the range finder includes:
 a first stage configured to determine a coarse range to the target; and 
 a second stage configured to determine a fine range to the target in response to the coarse range. 
 
     
     
       11. The apparatus of  claim 1  wherein the first algorithm is configured to model the target as not moving. 
     
     
       12. The apparatus of  claim 1  wherein the range finder includes at least one Kalman filter. 
     
     
       13. The apparatus of  claim 1  wherein the range finder includes at least one Kalman filter with all velocity component states having values fixed at zero. 
     
     
       14. The apparatus of  claim 13  wherein the range finder is configured to prompt an operator of the object to move the object in a manner that increases a speed at which the range finder can determine the range. 
     
     
       15. An apparatus, comprising:
 a detector configured to determine a direction to a target in response to a signal received from the target; and 
 a range finder configured to determine a range to the target in response to the direction and independently of an amplitude of the signal; 
 wherein the range finder includes: 
 
       a first Kalman filter configured to determine a first value of the range to the target; and 
       a second Kalman filter configured 
       to receive a seed parameter from the first Kalman filter, and 
       to determine a second value of the range to the target in response to the seed parameter. 
     
     
       16. An apparatus comprising: 
       a detector configured to determine a direction to a target in response to a signal received from the target; and
 a range finder configured to determine a range to the target in response to the direction and independently of an amplitude of the signal; 
 wherein the range finder includes: 
 a first Kalman filter configured to determine a first value of the range to the target; and 
 a second Kalman filter configured 
 
       to receive seed values for filter coefficients and filter variables from the first Kalman filter, and 
       to determine a second value of the range to the target in response to the seed values. 
     
     
       17. A tangible computer readable medium storing instructions that, when executed by a computing apparatus, cause the computing apparatus to perform, or cause the computing apparatus to cause another apparatus to perform, the following steps: 
       determining a direction to a target in response to a signal received from the target; and 
       determining a range to the target in response to only the direction;
 wherein the range to the target is determined by: 
 tracking the target according to a first algorithm; 
 tracking the target according to a second algorithm; 
 weighting results of the first and second algorithms; and 
 determining the range to the target in response to the weighted results of the first and second algorithms.